This invention relates to a focus adjustment mechanism for use with a video projector. Specifically, the invention provides a mechanism for focusing a projection lens which has two focusing elements which must be independently adjusted to focus an image on a displaced, generally planar screen.
Several types of video projectors are known. This invention is intended for use with a video projector which utilizes a single source image generator as opposed to plural, color generators. A single source generator produces an image which must be focused with different components of refraction at its central and peripheral portions. Generally, one or the other portions of the image is focused and the remaining portion is sequentially focused.
Known projection lenses utilize either push-pull or mutually rotatable elements which may be adjusted to focus portions of the image. Known lenses do not provide any means for retaining a focus setting on one lens element while another lens element is focused.
An object of the invention is to provide a focus adjustment mechanism which will slidably focus a first focusing element operable to focus a peripheral portion of a projected beam.
Another object of the invention is to provide a focus adjustment mechanism which will rotatably focus a central portion of a projected beam.
A further object of the instant invention is to provide a focus adjust mechanism which is easily accessible from the exterior of a video projector.
Yet another object of the invention is to provide a focus adjustment mechanism which is simple and easy to operate.
Another object of the invention is to provide a focus adjustment mechanism which is capable of retrofitting conventional focus mechanisms.
The instant invention includes a video projector having a frame and imaging means mounted on the frame. The imaging means generates a visually perceptible beam which has an image axis, and central and peripheral portions which must be focused independently of one another. The video projector includes a two-focusing element projection lens. Retaining means are provided to retain the projection lens non-rotatably on the frame. A first focusing element includes a lens carrying portion which is slidably and non-rotatably received on retaining means and which includes a sleeve. A second focusing element is rotatably received on the sleeve of the first focusing element. A first focusing means is operable to slidably focus the first focusing element and includes a bracket which is attached to the frame and a lever which pivots on the bracket and on the lens carrying portion, thereby to slide the lens carrying portion relative to the retaining means. Second focusing means is provided for rotatably focusing a second focusing element with rotation of the second element relative the first element.
These and other objects and advantages of the instant invention will become more fully apparent as the description which follows is read in conjunction with the drawings.